Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$91.38	10.326%	$100.8159	$100.82	$100.80	$100.80
Purchase #2	$246.82	4.402%	$257.685	$257.69	$257.70	$257.70
Purchase #3	$195.73	9.189%	$213.7156	$213.72	$213.70	$213.70
Purchase #4	$153.48	7.279%	$164.6518	$164.65	$164.65	$164.70
Purchase #5	$27.27	5.694%	$28.8228	$28.82	$28.80	$28.80
Purchase #6	$40.37	13.816%	$45.9475	$45.95	$45.95	$45.90
Purchase #7	$93.44	10.664%	$103.4044	$103.40	$103.40	$103.40
7 purchase totals =	$848.49		$915.0430	$915.05	$915.00	$915.00